The studies seem to suggest that intermittent fasting can result in similar weight loss and fat loss to continuous dieting. Muscle is preserved with Intermittent fasting, especially with high-protein. Intermittent fasting may not be optimal for increasing lean muscle mass.
DOES INTERMITTENT FASTING RESULT IN MUSCLE LOSS SUMMARY
- The studies suggest that intermittent fasting can result in similar weight loss and fat loss to continuous dieting.
- Muscle is preserved with Intermittent fasting, especially with high-protein.
- Intermittent fasting may not be optimal for increasing lean muscle mass.
An Introduction to Intermittent Fasting
Intermittent fasting has been advocated to be superior to conventional diets for boosting lean muscle mass and superior fat loss because of higher increases in Growth Hormone and other metabolic benefits. Intermittent fasting has benefits such as increased parameters of immune function and downfalls such as reduced anabolic hormones (i.e., decreased testosterone and IGF-1).(1) There are several forms of fasting: Alternate Day Fasting (i.e., eating every other day), Whole Day Fasting (i.e., fasting for 24 hours), and Time-Restricted Feeding (i.e., fasting for several hours at a time).
The most popular method of intermittent fasting to have positive changes in weight and fat loss appears to be 16 hours. Ramadan is the most widely accepted religious reason for fasting for Muslims, in which one does not eat from sunrise to sunset. During Ramadan, Muslims fast for 12-18 hours a day and do this for 30 days.
During Ramadan, food and liquid are only eaten at night. A recent meta-analysis of Ramadan and non-Ramadan intermittent fasting found that fasting can result in small decreases in fat and body weight. Still, the effect of these changes was mediated by the % body fat of the person starting the diet. Those with more body fat lost more weight and body fat during Ramadan than those with less body fat. The other interesting finding from the study was that Ramadan was not associated with loss of lean muscle.(2) This is contrary to the belief that intermittent fasting will cause muscle loss.
Studies on Intermittent Fasting
In a meta-analysis of intermittent fasting, some of the most common myths regarding fasting were debunked. One would suspect that fasting for 16 hours would result in low adherence and high dropout rates; however, intermittent fasting has similar dropout rates to traditional low-calorie dieting. The authors found that Intermittent fasting is safe and improves glycemia (i.e., blood sugar regulation). However, there is a potential for hypoglycemia (i.e., low blood sugar levels) that has been documented. Hunger levels remain stable or generally decrease with intermittent fasting.(3)
Several large-scale literature reviews have found that intermittent fasting is similar to calorie restriction, both equally reduced body weight, body fat, and changes in lean mass.(4-6) There is no “metabolic advantage” to intermittent fasting, as you commonly hear referred to by social media fitness influencers. Intermittent fasting is thus an alternative to calorie-restricted diets, but the outcomes are very similar for body composition (i.e., fat loss, weight loss, lean mass). The benefit of intermittent fasting is that it eliminates calorie counting throughout the day. Studies have shown that intermittent fasting with food restriction lasting 12-24 hours lost weight without counting calories.(7) Thus, intermittent fasting may be an easy way to create a caloric deficit compared to a continuous diet in which calories need to be meticulously calculated for the day.
INTERMITTENT FASTING RETAINS MUSCLE, BUT WHAT ABOUT BUILDING MUSCLE?
Intermittent fasting has been suggested to build lean muscle mass better than conventional dieting. A 2019 study by Tinsley et al. had the intermittent fasting community saying, “See, I told you so…intermittent fasting builds muscle!” Dr. Tinsley found that intermittent fasting produced similar increases in lean mass as a conventional diet. The study compared body composition changes from resistance training in three different conditions: a.) non-fasting (13.5-hour feeding window), Fasting (7.5-hour feeding window), and Fasting + HMB supplementation (7.5-hour feeding window). HMB has been reported to have anti-catabolic properties (i.e., reducing muscle loss), so the researchers wanted to see if HMB would preserve lean mass during intermittent fasting.
After eight weeks, all groups built a similar amount of muscle with no differences between the groups. If you do a deep dive into the methods sections, the intermittent fasting group consumed 4 meals per day which is not your typical intermittent fasting protocol. They consumed a protein shake before and immediately after exercise and then consumed two additional meals later on in the day. Most intermittent fasting protocols are limited to two meals a day (i.e., usually lunch and dinner). The normal diet group ate five meals a day. All groups consumed the same protein, calories, etc. This suggests that if you want to maintain muscle mass, having a protein shake pre and post-exercise and having your normal meals several hours later is a viable way to use intermittent fasting and maintain muscle mass.(8)
Other Studies on IF
Another study examined the 5:2 intermittent fasting diet in which you eat a normal diet Monday thru Friday, and then on Saturday and Sunday, you fast for 48 hours. Researchers had one group follow a continuous caloric deficit of 20%, and another follow a 5:2 intermittent fasting diet. The subjects didn’t in the 5:2 group didn’t fast completely for 48 hours. They dropped their calories to approximately 30% of their normal requirements (<600 calories). The subjects drank whey protein shakes, high protein stews, and raw vegetables between noon and six pm on the fasting days. This study used a high protein diet in both groups with protein intake at 1.4 g/kg/bw or .6 grams per pound of body weight. The subjects performed resistance exercises three times a week.
At the end of the study, both groups gained lean mass and lost body fat with no differences between the groups.(9) The ultrasound measurements for hypertrophy were intriguing; they found that the continuous dieting group had a small (non-significant) increase in leg growth compared to the 5:2 group. This study was conducted on untrained lifters. We don’t know if advanced lifters will respond the same way. The good news is that if you want to cut back on your calories just for two days, it seems you can lose body fat while preserving muscle.
ONE MEAL A DAY (OMAD) FOR MUSCLE MASS GAINS?
Lately, several athletes and Hollywood actors have said they eat one meal a day for longevity and health purposes in the news. A recent study examined one meal a day (i.e., at dinner between 5 and 7) versus three meals a day and its effect on body composition and performance in healthy adults. The calories were self-reported, which they calculated with a phone diet app. The subjects were allowed unlimited water, coffee, and tea (i.e., without sugar). There were no differences in the calories between the two groups at the end of the study. The researchers did several tests to measure aerobic capacity and strength tests. At the end of the two weeks, there were no differences in performance in either aerobic or strength capacity, but again, these were not lifters, just healthy living adults.
One meal a day increased fat oxidation (i.e., fat burning) after exercise and had lower blood glucose concentrations in the second half of the day. The one meal a day group lost more weight and more fat mass than the three meals a day group with no changes in lean mass (i.e., not statistically significant between the two groups). If you examine the lean mass, the one meal a day group lost -0.7 kg of muscle while the three meals a day group lost -0.3 kg of muscle.(10) This was only a 2-week study, but the one meal a day group was starting to move forward in the direction of losing more muscle mass.